Bond Day 2: #4

Chemical Bond Day 2: #4

Before there were bonds, there had to be elements Before there were bonds, there had to be elements! Let’s review elements & the Periodic Table No, not that table – THIS TABLE: Review the periodic table with the students. (Groups, periods, valence electrons) Day 2: #4

What are Chemical Bonds? An attraction between two or more atoms Interaction between valence electrons All atoms need 8 valence electrons to be “happy” or stable Day 2: #4

Two Kinds Ionic Bonds Covalent Bonds Form Ionic compounds (by losing /gaining electrons) Covalent Bonds Form Covalent compounds (by sharing electrons; “Co” means to share) Day 2: #4

How Do Ionic Compounds Form? metals (from groups 1,2,3 on the Periodic Table) combine with nonmetals (from groups 17, 16, 15). Day 2: #4

How Do Ions Form?…by losing or gaining - electrons Positive ions form, when valence electrons are lost (result = more + protons than – electrons which makes the charge +) Metals lose electrons, therefore: Group 1 metals: become +1 ions Group 2: +2 ions Group 3: +3 ions Day 2: #4

Lets look at Sodium to see how this is so … Sodium has 11 protons; 1 valence electron It is easier for Sodium to lose an electron to “be happy.” 11 p+ 10 e- 11 p+ 11 e- cation neutral +1 charge for sodium (Na) Day 2: #4

Ions can be negative too! Negative ions form when electrons are gained. (result = more - electrons than + protons which makes the charge -) Nonmetals gain electrons, therefore Nonmetals from Group 15: become - 3 ions Group 16: - 2 ions Group 17: - 1 ions Day 2: #4

Lets look at Oxygen 8 p+ 10 e- anion 8 p+ 8 e- neutral Oxygen has 8 protons; 6 valence electrons It is easier for oxygen to gain two electrons to “be happy.” O 8 p+ 10 e- anion 8 p+ 8 e- neutral - 2 charge for oxygen (O) Day 2: #4

…but how do ions BOND? The result is an ionic compound For ions the “bonding” refers to the giving and taking of electrons The result is an ionic compound Example:sodium (Na) gives 1 e and chlorine (Cl) takes it Na (+1) Cl (-1) NaCl  Day 2: #4

How do COVALENT bonds form? nonmetals (from groups 17, 16, 15) share valence electrons in order to obtain 8 total valence electrons and be “happy” Day 2: #4

How do nonmetals share? The sharing of electrons is either equal or unequal. Unequal sharing (polar covalent) Equal sharing (nonpolar covalent) Day 2: #4

Sharing to obtain 8 valence electrons….how does that look? C is in group 14 and has 4 valence electrons. Cl is in group 17 and has 7 valance electrons. By sharing, the C and each Cl is able to have 8 valence electrons! Day 2: #4

An unidentified element has many of the same physical and chemical properties as magnesium and strontium but has a lower atomic mass than either of these elements. What is the most likely identity of this element?   F Sodium G Beryllium H Calcium J Rubidium Answer:G Question from TEA released TAKS test Day 2: #4

The elements of which of these groups on the periodic table are most resistant to forming compounds?   A Group 1 B Group 9 C Group 14 D Group 18 Answer:D Question from TEA released TAKS test Day 2: #4

The elements from which of the following groups are most likely to react with potassium (K)?   F Group 2 G Group 7 H Group 13 J Group 17 Answer: J Question from TEA released TAKS test Day 2: #4

Which of the following groups contains members with similar chemical reactivity?   A Li, Be, C B Be, Mg, Sr C Sc, Y, Zr D C, N, O Answer: B Question from TEA released TAKS test Day 2: #4

According to the periodic table, which element most readily accepts electrons?   A Fluorine B Nitrogen C Arsenic D Aluminum   Answer: A Question from TEA released TAKS test Day 2: #4

Law of Conservation of Mass Matter cannot be created or destroyed in an ordinary chemical reaction. To show this all chemical equations must be balanced! When balancing an equation only coefficients can be added or changed. Subscripts cannot be changed! Example: 2NaCl → 2Na + Cl2 The 2’s in front of NaCl and Na are coefficients. The 2 below Cl is a subscript. Day 2-#3

Which chemical equation supports the law of conservation of mass? F 2H2O(l) → H2(g) + O2(g) G Zn(s) + HCl(aq) → ZnCl2(aq) + H2(g) H Al4C3(s) + H2O(l) → CH4(g) + Al(OH)3(s) J CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) Answer: J Day 2-#3 (All practice problems are from TEA released TAKS Tests)

Counting Atoms Name and Use Formula Atoms in Formula Silicon Dioxide Use: Sand SiO2 Si = Silicon 1 O = Oxygen 2 Calcium dihydrogen phosphate Use: fertilizer Ca(H2PO4)2 Ca=Calcium 1 H = Hydrogen 4 Phosphorous = 2 Oxygen = 8

Practice Problems: (All practice problems are from TEA released TAKS Tests) What are the coefficients that will balance this chemical equation? A 2, 1, 1 B 3, 4, 2 C 2, 2, 1 D 4, 3, 2 Answer: C Day 2-#3

What is the coefficient for H2O when the above equation is balanced? Answer: B Day 2-#3 (All practice problems are from TEA released TAKS Tests)

According to this information, what is the chemical formula for aluminum sulfate? A AlSO4 B Al2(SO4)3 C Al3(SO4)2 D Al6SO4 Answer: B Day 2-#3 (All practice problems are from TEA released TAKS Tests)

B The sum of the products’ masses is less than the mass of the CaCO3. The chemical equation shows CaCO3 being heated. Which of these statements best describes the mass of the products if 100 g of CaCO3 is heated? A The difference in the products’ masses is equal to the mass of the CaCO3. B The sum of the products’ masses is less than the mass of the CaCO3. C The mass of each product is equal to the mass of the CaCO3. D The sum of the products’ masses equals the mass of the CaCO3. Answer: D Day 2-#3 (All practice problems are from TEA released TAKS Tests)

The chemical formula for calcium chloride is — F Ca2Cl G CaCl H CaCl2 J Ca2Cl3 Answer: F Day 2-#3 (All practice problems are from TEA released TAKS Tests)

When 127 g of copper reacts with 32 g of oxygen gas to form copper (II) oxide, no copper or oxygen is left over. How much copper (II) oxide is produced? F 32 g G 95 g H 127 g J 159 g Answer: J Day 2-#3 (All practice problems are from TEA released TAKS Tests)

When the above equation is balanced, the coefficient for magnesium chloride is — A 0 B 1 C 2 D 4 Answer: B Day 2-#3 (All practice problems are from TEA released TAKS Tests)

According to the law of conservation of mass, how much zinc was present in the zinc carbonate? A 40 g B 88 g C 104 g D 256 g Answer: C Day 2-#3 (All practice problems are from TEA released TAKS Tests)

Elements in Group 16 of the periodic table usually —   F form large molecules G gain electrons when bonding H act like metals J solidify at room temperature Answer: G Question from TEA released TAKS test Day 2: #4